Paul Golding, the former leader of far-right political party Britain First, has been released from prison after being jailed for carrying out one of the group's so-called "mosque invasions".
Golding, 34, served four weeks of his eight-week sentence at HMP Pentonville in north London and was released on 11 January.
The acting Britain First leader, Jayda Fransen, claimed Golding, who would have been a high-profile inmate, had been placed in 23-hour lockdown during his time behind bars.
The most recent prison inspection report, from 2015, found HMP Pentonville to be "unsafe" with levels of violence "much higher than in similar prisons". It also struggled with "gang-related issues", the report said, and left inmates suffering "filthy cells" and without access to daily showers, clean clothes or eating utensils.
Golding's time in HMP Pentonville came after he pleaded guilty to breaching a High Court injunction on 15 December 2016 following an incident in August that year at Al-Manar Islamic Centre in Cardiff.
The "mosque invasion" saw Golding film his activists from outside the mosque as they grilled worshippers inside the Islamic centre over allegations, printed in a national newspaper the previous month, that their Imam was a "radical preacher".
The incident was said to have caused "serious harassment, alarm or distress" to worshippers at the mosque.
Golding admitted his involvement in the incident breached a civil High Court injunction granted to Bedfordshire Police a week before, on 11 August, which prohibited him from entering, or encouraging others to enter, any mosque in England and Wales for three years.
The police force had sought the injunction after arguing the party had caused "community tensions" with their anti-Islam activism in Luton.
Sentencing him at the High Court, Judge Moloney had told Golding the breach was "a deliberate and cynical defiance of a court order" that had been designed to "protect Muslim communities".
Before being sentenced, Golding's defence, Neil Guest, said his client offered his "full and unreserved" apology for the breach, adding that his party would not engage in so-called "mosque invasions" in the future.
He said Golding had not deliberately gone against the terms of the injunction, but had simply not understood them - something the judge later said he was satisfied was "not true".
Guest added that Golding was no longer as politically active as he had been, having recently stepped down as leader of Britain First for family reasons. He remains a member of the party, he added.